1. Field of the Invention
The present invention concerns a air suction lifter, more precisely a lifter for moving packages by means of the suction created inside a chamber by a source of vacuum. In greater detail, the invention concerns a suction lifter specially designed to be used safely and reliably on non-rigid packaging such as cloth or paper sacks and the like.
2. Description of the Prior Art
The suction lifters known at present consist of a single suction chamber which is generally cylindrical in shape, with one open end, across which a part of the surface of the package is subject to suction and deformation. Inside the suction chamber, parallel to the open base, there is a perforated plate, or limiter. This structure bears against and retains the area of the upper face, subject to suction and deformation, of the package or sack to be moved i.e. lifted, transported or deposited. To try to conserve the high value of the low pressure inside the suction chamber after the grip on the package has been established and maintained, the lower edge of the outside walls of the suction chamber are fitted with air-tight elements e.g. seals. Once the vacuum has been established and an area of the surface of the package has been gripped, the package is moved as desired and later released by interruption of the suction.
The main drawback of the traditional lifting device as above illustrated is the ineffective seal obtained between the edge of the suction chamber and the package, especially if the package is a sack (which is so in the majority of cases).
Actually, creases or folds on the upper surface of the sack, especially in the area involved in the suction, are formed which can extend into the area in contact with the aforementioned perforated plate and pass under the airtight seal means.
In this way the folds connect the suction chamber to the outside atmosphere and drastically reduce the level of vacuum in the suction chamber. Because of said reduction, the flow rate of air snoked from the chamber has to be considerably increased to maintain the grip on the package or sack in question. Despite this, the hold on the sack remains precarious and it is often sufficient just to jolt the sack while it is suspended to alter negatively the balance between the air entering the chamber and the sucked air, thus causing the sack being lifted to fall. Further, because of the difficulties described above, the equipment required to guarantee a sufficient suction is so large that it can be moved only with great difficulty, thus detracting from the flexibility required of similar devices.
Finally, because of the stated disadvantages, different sized suction chambers are required depending on the kind of packages (sacks) to be moved.
There is then a necessity for a suction lifter which safely moves non-rigid packages, and in particular sacks of different sizes. Further, such lifter should be operated by vacuum sources that are sufficiently small to be easily moved.